Ni-rich Oxide Cathode Research Articles

High-rate and long-life Ni-rich oxide cathode under high mass loading for sulfide-based all-solid-state lithium batteries

The interface side reaction and mechanical failure are the main factors affecting electrochemical performances of Ni-rich oxide cathode for sulfide-based all-solid-state lithium batteries (ASSLBs). It is believed that the interface side reaction is mainly caused by the high nickel content and residual lithium compounds on the surface, and the mechanical failure is mainly caused by severe volume change during cycling. In view of this, core-shelled Ni-rich Li(Ni0.9Mn0.05Co0.05)0.8Co0.2O2 is constructed and further modified with Al source. In this strategy, the core-shell structure design of Ni-rich oxide material can decrease the surface nickel content and reduce the volume change, and the surface modification process of core-shelled Ni-rich oxide material with aluminum isopropoxide can generate Al-modifying layer (Al2O3 and LiAlO2 layer), which will not only remove the lithium compounds but also form the coating layer. Under high mass loading of 36.94 mg cm−2, Al-modified Li(Ni0.9Mn0.05Co0.05)0.8Co0.2O2 (CS-NCM@Al) cathode displays the discharge capacity of 158.6 mAh g−1 at 0.2 C with high initial coulombic efficiency of 88.3%. More significantly, it shows a significant capacity retention of 96.3% after 500 cycles at 1 C (7.39 mA cm−2). This work opens up a new avenue for meeting the future application of high energy density sulfide-based ASSLBs.

Research progress of solid polymer electrolyte/high voltage cathode interphase stability

<p indent=0mm>Solid polymer electrolytes (SPEs) are promising candidates for next-generation energy storage because of their excellent mechanical properties, weather resistance and easy processing. They are better than those of inorganic solid electrolytes (ISEs). Moreover, compared with liquid electrolytes, SPEs also perform a better thermal stability. However, the practical application of SPEs has been impeded by the interphase issues of electrodes/SPEs, especially, the high-capacity cathodes/SPEs interphase in a high energy density battery system. Here we review the key characteristics of SPEs and the interphase issues of high-voltage cathode/SPEs, including the poor interphase contact and interphase instability. In addition, we further analyze the main factors that lead to the serious interphase problems between high-voltage Ni-rich oxide cathodes and SPEs. The effective strategies to solve these problems are also summarized. Finally, we propose a prospect for the improvement of high-voltage Ni-rich cathode/SPE interphase, which provides a guideline for future research on solid Li batteries.

Understanding the Relationship between State-of-Charge and Structural Fragility in Ni-Rich Layered Materials for Lithium Batteries

Lithium batteries are at the frontier of energy storage. Co-free, Ni-rich layered transition metal oxide (TMO) materials have gained interest within the past decade due to their low cost and increased practical capacity. The challenge with employing these layered oxide cathodes is their inherent structural fragility, facilitated by metal cation migration and lattice oxygen loss. Upon charging, the redox center becomes oxidized, generating thermodynamically favorable electron transfer pathways between the electrolyte and the layered oxide. This transfer pathway is mainly due to the TM3d-O2p orbital hybridization perturbation during battery charging.Surface reconstruction and the structural reordering that accompanies it can undesirably influence the cathode – electrolyte interphase, leading to enhanced electrolyte degradation pathways that can minimize Coulombic efficiency. Electrolyte decomposition occurs at the oxide cathode surface, but can lead to bulk electronic and structural changes of the layered oxide, chemomechanical breakdown, and irreversible phase transformations.In this study, we focus on understanding the interplay between bulk phase transitions and surface instability with respect to electrolyte chemical decomposition. We use novel galvanostatic cycling parameters, extensive electron microscopy, and synchrotron X-ray techniques to decouple chemical and electrochemical electrolyte decomposition pathways to understand their role in Co-free, Ni-rich oxide cathode degradation. This work allows us to decouple surface and bulk chemistries at the cathode – electrolyte interphase to inform further insight into optimal Ni-rich oxide cathode design.

Graphene/PVDF Composites for Ni-rich Oxide Cathodes Toward High-Energy Density Li-ion Batteries.

Li-ion batteries (LIBs) employ porous, composite-type electrodes, where few weight percentages of carbonaceous conducting agents and polymeric binders are required to bestow electrodes with electrical conductivity and mechanical robustness. However, the use of such inactive materials has limited enhancements of battery performance in terms of energy density and safety. In this study, we introduced graphene/polyvinylidene fluoride (Gr/PVdF) composites in Ni-rich oxide cathodes for LIBs, replacing conventional conducting agents, carbon black (CB) nanoparticles. By using Gr/PVdF suspensions, we fabricated highly dense LiNi0.85Co0.15Al0.05O2 (NCA) cathodes having a uniform distribution of conductive Gr sheets without CB nanoparticles, which was confirmed by scanning spreading resistance microscopy mode using atomic force microscopy. At a high content of 99 wt.% NCA, good cycling stability was shown with significantly improved areal capacity (Qareal) and volumetric capacity (Qvol), relative to the CB/PVdF-containing NCA electrode with a commercial-level of electrode parameters. The NCA electrodes using 1 wt.% Gr/PVdF (0.9:0.1) delivered a high Qareal of ~3.7 mAh cm−2 (~19% increment) and a high Qvol of ~774 mAh cm−3 (~18% increment) at a current rate of 0.2 C, as compared to the conventional NCA electrode. Our results suggest a viable strategy for superseding conventional conducting agents (CB) and improving the electrochemical performance of Ni-rich cathodes for advanced LIBs.

Charge/discharge cycling of Li1+x(Ni0.6Co0.2Mn0.2)1−xO2 primary particles performed in a liquid microcell for transmission electron microscopy studies

Ni-rich layered oxides are promising positive electrodes for fulfillment of government and industry targets for lithium-ion-battery-operated electric mobility purposes. Apart from ongoing research focusing on their design and material production, advanced characterization techniques can provide valuable insights on their stabilization by monitoring in situ the degradation mechanisms. Herein, we use liquid-phase transmission electron microscopy to examine the effects of electrochemical stimuli on Ni-rich oxide cathodes by introducing an optimized micro-scale battery configuration. Ball-milled Li1+x(Ni0.6Co0.2Mn0.2)1−xO2 (NCM622) particles were cycled against a delithiated LiFePO4 anode and the effects of different cycling methods were investigated. We show that commonly used cyclic voltammetry measurements at high scan rates cannot be used to simulate battery operation in situ due to geometry limitations of the cell that inhibits Li ion transport. However, using galvanostatic charge/discharge cycling and introducing a pause every 10 cycles for a total of 50 cycles results in degradation in the form of Mn and Co ion dissolution from the first 20 nm of the surface. Our results suggest that although performing battery cycling using liquid cell electron microscopy may differ from the case of coin cells, by tuning the electrochemical profiles used similar degradation mechanisms can be attained.

High Volumetric Energy Density Sulfur Cathode with Heavy and Catalytic Metal Oxide Host for Lithium-Sulfur Battery.

For high‐energy lithium–sulfur batteries, the poor volumetric energy density is a bottleneck as compared with lithium–ion batteries, due to the low density of both the sulfur active material and sulfur host. Herein, in order to enhance the volumetric energy density of sulfur cathode, a universal approach is proposed to fabricate a compact sulfur cathode with dense materials as sulfur host, instead of the old‐fashioned lightweight carbon nanomaterials. Based on this strategy, heavy lanthanum strontium manganese oxide (La0.8Sr0.2MnO3), with a high theoretical density of up to 6.5 g cm−3, is introduced as sulfur host. Meanwhile, the La0.8Sr0.2MnO3 host also acts as an efficient electrocatalyst to accelerate the diffusion, adsorption, and redox dynamics of lithium polysulfides in the charge–discharge processes. As a result, such S/La0.8Sr0.2MnO3 cathode presents high gravimetric/volumetric capacity and outstanding cycling stability. Moreover, an ultra‐high volumetric energy density of 2727 Wh L−1 ‐cathode is achieved based on the densification effect with higher density (1.69 g cm−3), which is competitive to the Ni‐rich oxide cathode (1800–2160 Wh L−1) of lithium–ion batteries. The current study opens up a path for constructing high volumetric capacity sulfur cathode with heavy and catalytic host toward practical applications of lithium–sulfur batteries.

(Invited) Understanding Chemical, Mechanical and Thermal Stability of NCA in Polymer Solid-State Batteries

The structural integrity and chemical stability of layered Ni-rich oxide cathode materials are influential factors that critically affect the performance and reliability of lithium batteries. Prolonged battery operation often involves repeated phase transitions, buildup of mechanical stresses, which could result in chemical and mechanical changes in cathodes. Chemo-thermo-mechanical interplay can cause performance degradation through various processes. Here we systematically investigate such complex chemomechanical and chemothermal interplays over a wide range of length scales within the hierarchically structured polymer solid-state batteries. This presentation will discuss our understanding of 1) The formation of mesoscale cracks and corresponding state of charge (SOC) inhomogeneity within secondary NCA particle cycled in solid polymer batteries1 2) Thermal decomposition, fracture (intergranular and intragranular), and mesopores formation due to oxygen evolution in delithiated Li0.30NCA particles upon heating2 3) long-term chemothermal stability of delithiated Li0.30NCA at relevant operating conditions of polymer solid-state batteries.3 Our investigation provides a fundamental understanding of chemo-thermo-mechanical breakdown of the NCA in solid-state polymer batteries.Reference : 1. Besli, M. M. et al. Mesoscale Chemomechanical Interplay of the LiNi0.8Co0.15Al0.05O2 Cathode in Solid-State Polymer Batteries. Chem. Mater. 31, 491–501 (2019).2. Besli, M. M. et al. Thermally-driven mesopore formation and oxygen release in delithiated NCA cathode particles. J. Mater. Chem. A 7, 12593–12603 (2019).3. Besli, M. M. et al. Long-Term Chemothermal Stability of Delithiated NCA in Polymer Solid-State Batteries. J. Mater. Chem. A 11–13 (2019) doi:10.1039/c9ta11103d.

O3-Type Layered Ni-Rich Oxide: A High-Capacity and Superior-Rate Cathode for Sodium-Ion Batteries.

Inspired by its high-active and open layered framework for fast Li+ extraction/insertion reactions, layered Ni-rich oxide is proposed as an outstanding Na-intercalated cathode for high-performance sodium-ion batteries. An O3-type Na0.75 Ni0.82 Co0.12 Mn0.06 O2 is achieved through a facile electrochemical ion-exchange strategy in which Li+ ions are first extracted from the LiNi0.82 Co0.12 Mn0.06 O2 cathode and Na+ ions are then inserted into a layered oxide framework. Furthermore, the reaction mechanism of layered Ni-rich oxide during Na+ extraction/insertion is investigated in detail by combining ex situ X-ray diffraction, X-ray photoelectron spectroscopy, and electron energy loss spectroscopy. As an excellent cathode for Na-ion batteries, O3-type Na0.75 Ni0.82 Co0.12 Mn0.06 O2 delivers a high reversible capacity of 171 mAh g-1 and a remarkably stable discharge voltage of 2.8 V during long-term cycling. In addition, the fast Na+ transport in the cathode enables high rate capability with 89 mAh g-1 at 9 C. The as-prepared Ni-rich oxide cathode is expected to significantly break through the limited performance of current sodium-ion batteries.

LiNbO3-coated LiNi0.8Co0.1Mn0.1O2 cathode with high discharge capacity and rate performance for all-solid-state lithium battery

Abstract In order to obtain high power density, energy density and safe energy storage lithium ion batteries (LIB) to meet growing demand for electronic products, oxide cathodes have been widely explored in all-solid-state lithium batteries (ASSLB) using sulfide solid electrolyte. However, the electrochemical performances are still not satisfactory, due to the high interfacial resistance caused by severe interfacial instability between sulfide solid electrolyte and oxide cathode, especially Ni-rich oxide cathodes, in charge-discharge process. Ni-rich LiNi0.8Co0.1Mn0.1O2 (NCM811) material at present is one of the most key cathode candidates to achieve the high energy density up to 300 Wh kg−1 in liquid LIB, but rarely investigated in ASSLB using sulfide electrolyte. To design the stable interface between NCM811 and sulfide electrolyte should be extremely necessary. In this work, in view of our previous work, LiNbO3 coating with about 1 wt% content is adopted to improve the interfacial stability and the electrochemical performances of NCM811 cathode in ASSLB using Li10GeP2S12 solid electrolyte. Consequently, LiNbO3-coated NCM811 cathode displays the higher discharge capacity and rate performance than the reported oxide electrodes in ASSLB using sulfide solid electrolyte to our knowledge.

Improving the reversibility of the H2-H3 phase transitions for layered Ni-rich oxide cathode towards retarded structural transition and enhanced cycle stability

Although the layered Ni-rich LiNixCoyMn1-x-yO2 (0.7 < x < 1, 0 < y < 0.3) cathode materials are expected to deliver high capacity, their moderate cycle lifetime and thermal stability still hinder practical applications. There's often a tradeoff between high capacity and structure stability since more Li+ ions delithiated during charging will leave the structure of the layered Ni-rich materials more vulnerable. Herein, we propose that improving the reversibility of H2-H3 phase transition for Ni-rich materials is effective to tackle this challenge. It has been confirmed that the generation of microcracks and structural transformations have been suppressed since the H2-H3 phase transition becomes reversible, while which shows little effect on capacity delivery. Consequently, using Ni-rich LiNi0.9Co0.1O2 as the cathode material, the 100th capacity retention cycling at 38 mA g−1 has been improved remarkably from 69.7% to 97.9% by adopting this strategy. Hence, it should be a novel solution to realize both high capacity and stable cyclability for the Ni-rich cathodes.

Thermally-driven mesopore formation and oxygen release in delithiated NCA cathode particles

The structural integrity of layered Ni-rich oxide cathode materials is one of the most essential factors that critically affect the performance and reliability of lithium-ion batteries.

Interfacial Stability of Argyrodite-Based Solid Electrolytes in All-Solid-State Batteries

All-solid-state batteries (ASSBs) are currently attracting much attention as next generation energy storage systems, with potentially both higher energy and power densities than state-of-the-art lithium-ion batteries (LIBs). The latter may be realized by combining layered Ni-rich oxide cathode materials such as Li1+x (Ni1 – y – z Co y Mn z )1 – x O2 (NCM) and thiophosphate-based solid electrolytes (SEs). As for SEs, in particular argyrodites, Li6PS5X (X = Cl, Br), show great promise since they exhibit sufficient Li-ion conductivity (~2 mS/cm) and because of the simplicity of preparation.1 However, their practical implementation is hindered by poor electrochemical stability at the interface, in particular with positive electrode materials.2,3 In order to pave the way for rational interface design, processes occurring between cathode and electrolyte need to be better understood. Following these guiding principles, we herein report our recent efforts in implementing various in situ and ex situ techniques (X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, differential electrochemical mass spectrometry etc.) to gain mechanistic insight into interfacial SE degradation when in direct contact with NCM622 (60% Ni). We reveal the potential resolved formation of degradation products, which are found to be responsible in part for irreversible capacities and performance decay of ASSB cells. However, we also demonstrate that by using protective oxide coatings such as LiNbO3, these detrimental side reactions can be suppressed to a large extent. In summary, we reveal the importance of developing in situ characterization techniques in the area of ASSBs and provide valuable insight into the cathode/SE interfacial chemistry.

Impact of Cathode Material Particle Size on the Capacity of Bulk-Type All-Solid-State Batteries

The implementation of all-solid-state batteries (ASSBs) is regarded as an important step toward next-generation energy storage systems, in particular for electric vehicles and portable electronics. This may be achieved through application of layered Ni-rich oxide cathode materials such as Li1+x(Ni1–y–zCoyMnz)1–xO2 (NCM) with high specific capacity and thiophosphate-based solid electrolytes. Here, the profound effect that the secondary particle size of the cathode active material has on the capacity of ASSB cells comprising NCM622 (60% Ni), β-Li3PS4, and In anode is demonstrated. We show the benefits of using small particles (d ≪ 10 μm), allowing virtually full charge capacity. This finding is rationalized through galvanostatic charge–discharge tests and complementary ex situ and operando X-ray diffraction experiments combined with Rietveld refinement analysis. Our results indicate the importance of considering and avoiding electrochemically inactive electrode material in bulk-type ASSBs, which we show usi...

Effect of Silyl Ether-functinoalized Dimethoxydimethylsilane on Electrochemical Performance of a Ni-rich NCM Cathode.

Dimethoxydimethylsilane (DODSi) is used as an interface stabilizing additive through a selective HF scavenging reaction for layered Ni-rich oxide cathodes. Ex situ NMR analyses demonstrated that DODSi effectively removes HF from the electrolyte based on the matched chemical reactivity of Si with F- and O with H+ . The cells employing DODSi exhibit higher specific capacity with retention than those cycled with a DODSi-free electrolyte even under in situ HF generating conditions. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma-mass spectroscopy (ICP-MS) analyses indicate that DODSi effectively protects the Ni-rich oxide cathodes against HF corrosion, resulting in improved surface stability of Ni-rich cathodes.

Core/Double-Shell Type Gradient Ni-Rich LiNi0.76Co0.10Mn0.14O2 with High Capacity and Long Cycle Life for Lithium-Ion Batteries.

A concentration-gradient Ni-rich LiNi0.76Co0.1Mn0.14O2 layered oxide cathode has been developed by firing a core/double-shell [Ni0.9Co0.1]0.4[Ni0.7Co0.1Mn0.2]0.5[Ni0.5Co0.1Mn0.4]0.1(OH)2 hydroxide precursor with LiOH·H2O, where the Ni-rich interior (core) delivers high capacity and the Mn-rich exterior (shells) provides a protection layer to improve the cyclability and thermal stability for the Ni-rich oxide cathodes. The content of nickel and manganese, respectively, decreases and increases gradually from the center to the surface of each gradient sample particle, offering a high capacity with enhanced surface/structural stability and cyclability. The obtained concentration-gradient oxide cathode exhibits high-energy density with long cycle life in both half and full cells. With high-loading electrode half cells, the concentration-gradient sample delivers 3.3 mA h cm(-2) with 99% retention after 100 cycles. The material morphology, phase, and gradient structure are also maintained after cycling. The pouch-type full cells fabricated with a graphite anode delivers high capacity with 89% capacity retention after 500 cycles at C/3 rate.

Suppressing the Phase Transition of the Layered Ni-Rich Oxide Cathode during High-Voltage Cycling by Introducing Low-Content Li2MnO3.

The layered Ni-rich oxide cathode (LiNi0.8Co0.1Mn0.1O2) suffers from a tremendous structural degradation during high-voltage cycling (4.8 V), causing the drastic rise of electrode impedance and deterioration of the capacity retention. Here, we develop an effective strategy to overcome these problems of the Ni-rich cathode material through doping low-content Li2MnO3 as an excellent structure stabilizer. Cyclic voltammogram and ex-situ X-ray diffraction measurements have reveled that Li2MnO3 could display a remarkable suppression effect on the phase transition of LiNi0.8Co0.1Mn0.1O2. The electrochemical tests showed that Li2MnO3-stabilized LiNi0.8Co0.1Mn0.1O2 could realize the large reversible capacity, stable discharge voltage and excellent cycling life during high-voltage cycling, which could be benefited from the enhanced structural stability of the modified Ni-rich cathode. The Li2MnO3 could sufficiently suppress the phase transition between two hexagonal phase (H2 and H3) with distinctly different lattice parameters, significantly reducing variation of unit-cell volume, which facilitates stabilization of the original layered structure of LiNi0.8Co0.1Mn0.1O2 cathode during high-voltage cycling.

Enhancement on the Cycling Stability of the Layered Ni-Rich Oxide Cathode by In-Situ Fabricating Nano-Thickness Cation-Mixing Layers

The layered Ni-rich oxide cathode (LiNi0.8Co0.1Mn0.1O2) has been significantly attractive due to its large reversible capacity (200 mAh g−1). However, the layered Ni-rich oxide cathode suffers from a tremendous structural degradation during long-term cycling, causing the drastic rise of electrode impedance and deterioration of the capacity retention. In this paper, we develop a novel and facile approach to stabilize its structure by per-cycling of the layered Ni-rich oxide cathode at high voltage of 4.5 V (vs Li/Li+). The nano-thickness cation-mixing layers with Fm-3m structure were in-situ formed on the layered Ni-rich oxide LiNi0.8Co0.1Mn0.1O2 cathode by the surface structural transition from rhombohedral phase to cubic phase. The as-prepared LiNi0.8Co0.1Mn0.1O2 cathode coated with the nano-thickness cation-mixing layers shows superior cycling life at a cutoff voltage of 4.3 V, and it keeps a capacity retention of 83% after 500 cycles, which could be attributed to that the nano-thickness cation-mixing layers stabilize the structure of LiNi0.8Co0.1Mn0.1O2 during long-term cycling.

Improving the Cycling Performance of the Layered Ni-Rich Oxide Cathode by Introducing Low-Content Li2MnO3

The layered Ni-rich oxide LiNi0.8Co0.1Mn0.1O2 cathode has been significantly attractive due to its large reversible capacity (∼200mAhg−1). However, the inherent poor cycling stability of the Ni-based cathode materials is always a serious issue for restricting its commercialization. In this paper, we introduced Li2MnO3 as an electrochemical inactive component in Ni-rich oxide LiNi0.8Co0.1Mn0.1O2 to stabilize its structure. The modified LiNi0.8Co0.1Mn0.1O2 composites with low-content Li2MnO3 were prepared by a solid-state reaction process. The results from XRD structure refinement and SAED confirm that Li2MnO3 phase exists homogeneously in the composites. The modified LiNi0.8Co0.1Mn0.1O2 composites with inactive Li2MnO3 show much better cycling stability and stable average discharge voltage compared with the pristine one when charged to 4.5V. Especially, the modified LiNi0.8Co0.1Mn0.1O2 composite with 10% Li2MnO3 (LNCMO-1090) delivers a reversible capacity of 207mAhg−1 and keeps 155mAhg−1 after 100 cycles at 20mAg−1 (0.1C), corresponding to a capacity retention of 75%, while LiNi0.8Co0.1Mn0.1O2 could only maintain a capacity of 128mAhg−1 with a capacity retention of 59% after 100 cycles. The improved cycling performance of the Li2MnO3-containing electrode could be attributed to the stabilized effect of Li2MnO3 on the electrode surface structure, as evidenced by the lower charge-transfer resistance.